Topband: Cushcraft MA-160

[Guy Olinger K2AV]

Not that I ever used  one of those, When I was a teenager the "old" hams
who were in the signal corp talked about antennas they used in WWII (God
bless 'em all).

The crow's foot comes from hanging the vertical up one side of a tree up to
a support point, and pulling top loading away in the only direction(s)
 available.  No electrical intentionality in pulling them all to one side.
 They THOUGHT that enhanced radiation in the direction of the crow's feet.
 They were in fact wrong about that, as any 1/4 wave "L-ish" antenna has a
mild 1-2 dB advantage AWAY from the bend to the horizontal.  But they
didn't have EZNEC back then to tell them these things.  The important thing
was that the upper crow's feet increased the signal strength and made it
easier to tune, and they DID know that.  That it let out some of that
dag-nabbed, commie-pinko, stinky, ugly horizontal polarization was beside
the point.

Also of note, these guys were not thinking 160 meters.  They typically used
frequencies from 500 kc to 8 mc, and would use different frequencies across
24 hours, and these edge of jungle up on a mountain stations could get up
one wire, then have to pull it down to move station and wire (which they
had to reuse, just like the radio) to avoid enemy movements.  Putting wire
through the middle of trees got you snaggled.  Cord could be replaced with
parachute cord which was everywhere from supply drops.  Wire was precious,
and like equipment.

As to 160, very few antennas on 160 have the current max anywhere except
right at the junction between radiator and radials.  Therefore the current
at top is reduced and the free end of a horizontal part is the current
minimum, AND therefore never comes close to carrying the majority of the
current.  For 160 contesters (where stateside contacts always count for a
large part of your score) that extra horizontal radiation fills in a  blind
spot above 45 degrees that fills in skip zones.  A purely vertical antenna
has a huge, deep notch in all directions above 45 degrees.

The huge problem with slopers is when they are supported by a tower.  It is
trivial to construct a very typical small tower setup with a sloper, where
there is MORE current IN THE TOWER, than in the sloper, making the base
treatment of the tower critical for avoiding hard coupling the dirt at the
tower base as a  parallel dummy load resistor.  This loss in addition to
any from unintended changes in pattern.  Then you are into somehow creating
a dense radial system for the tower base.

Either load the tower or get away from it.  IMHO slopers work better in
trees.  Before I had a tower at current QTH, I had a 40m sloping folded
dipole toward the NW.  It was a GREAT stateside antenna for whole US.
 Putting up a tower in roughly same corner of lot, and hanging the sloper
off the tower, turned a marvelous 40m sweepstakes antenna into a piece of
crap.  Later, getting into modeling, I discovered that when I explicitly
modeled the tower and every conductor, that the tower had turned a 3 dBi
antenna with 270 degree coverage into a -8 dBi antenna with most of its
radiation above 50 degrees.  In the model, the TOWER was carrying MORE
CURRENT than the sloper.

There is no magic in funny elevated radials. You are either dense and
uniform or you are not.  Lacking the commercial grade solutions, you are
left to come up with a counterpoise that minimizes ground losses.  In the
WWII situation you are left with needing something that first of all you
can load up across all the needed frequencies.  1625 tetrode final amps (12
volt 807's) in ARC-5's and that big roller coil were a big help.  Forget
SWR.  What you wanted was antenna current.  Current in the antenna worked.
 More current in antenna meant bigger signal.  The Crow's feet increased
the antenna current.

The FCP would not have worked for the WWII guys.  FCP only works on a
single band of frequencies.  The crows foot stuff would have broad-banded
the antenna to help it with working 100 kc to 8 mc.

73, Guy.

On Tue, Mar 20, 2012 at 6:45 AM, Herb Schoenbohm <herbs at vitelcom.net> wrote:

>  Paul,
>
> I really don't know if it makes a difference as the top wire is only
> supposed to do top loading and the goal is to minimize high angle radiation
> from the horizontal portion.  I saw the crow's foot antenna in a US
> Military Antenna book once and it had three on the top and three wires on
> the bottom Marconi style feed.  Maybe this would be a good configuration
> for someone to model. Personally I prefer the Marconi T with a symmetric
> ground system.  Maybe Guy K2AV has had some experience  with the three over
> three crows foot spread for top band. This seems to be right up his alley.
>
>
> Herb, KV4FZ
>
>
>
>
>
> On 3/20/2012 12:20 AM, Paul Lambert wrote:
>
> Hey Herb,
>
>  Enjoy all your replies and articles.
>
>  Old question for you. With an inverted "L" is there a
> favorite direction with the "L" or the opposite direction?
>
> Had a "crows-foot" many years ago an remember the
> direction went with the "L" direction.
>
>    _________________________
> II_________________________
>  II_________________________
> II
> II
> II
> II
> II
> II
> (.)------------------------------------------------------------coax to
> shack
> on the ground radials
> ____________________________
> ____________________________
> ____________________________
>
>  The Crow's Foot story is from an old Marine "Forward Observer"
>  experienced in the S. Pacific during WWII. A story for another time.
>
>  Anyway, what do you think or know?
>
>  Thank you,
>
>  73, Paul
> N8ABS
>  --------------------------------------------------I
>  On Sat, Mar 17, 2012 at 7:50 AM, Herb Schoenbohm <herbs at vitelcom.net>wrote:
>
>> Dave,
>>  If you ground the top of the wire of a quarter-wave sloper to the tower
>> and feed the bottom of the slant wire instead (assuming a ground rod and
>> some radials laying on the ground at the feed point) you will IMHO do
>> much better. Some matching may be required at the feed point but it may
>> be no more than a series capacitor to remove the reactance of the wire.
>> There my be a very slight bit of directivity in the direction of the
>> slant wire,  but the overall efficiency of this as a TB radiator may be
>> significantly better even with a short tower of 50-60 feet.  If the
>> tower is more than 60 feet tall and with a beam on top I would suggest
>> shunt feeding the tower with a cage feed again assuming you can have at
>> least 4 or more radials on the ground even if you need to fold or bend
>> the ends a bit to fit in your yard.
>>
>> All half slopers from metal towers do IMHO is try to backward excite the
>> tower with RF.  Losses can be high and performance is generally less
>> than adequate.  If you are able to shorten the slant wire to get your
>> feed point closer to 50 ohms may also be beneficial and should also be
>> considered.
>>
>> Good luck,
>>
>> Herb Schoenbohm, KV4FZ
>>
>>
>>
>>
>> On 3/16/2012 10:57 PM, David Novoa, W4DN wrote:
>> > Has anyone in this reflector installed a Cushcraft  MA-160 short
>> vertical
>> > with a couple of  elevated radials or the K2AV Folded Counterpoise?  If
>> > so, results? Any  recommendations?  I need to do something before the TB
>> > season ends.  My quarter-wave sloper doesn't work properly.
>> > Thanks,
>> > Dave, W4DN
>> >
>> >
>> > _______________________________________________
>> > UR RST IS ... ... ..9 QSB QSB - hw? BK
>>
>> _______________________________________________
>> UR RST IS ... ... ..9 QSB QSB - hw? BK
>>
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